<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        .father{
            width: 300px;
            height: 300px;
            background-color: cadetblue;
            /* display: flex; */
            /* 垂直居中 */
            /* align-items: center; */
            /* 水平居中 */
            /* justify-content: center; */

            position: relative;
            
        }
        .son{
            width: 50px;
            height: 50px;
            background-color: cornflowerblue;
            position: absolute;
            top: 50%;
            left: 50%;
            transform: translate(-50%, -50%);
        }
    </style>
</head>
<body>
    <div class="father">
        <div class="son">

        </div>
    </div>
</body>
</html>